Effects and Signal Processors - Gate

This circuit allows input signals to reach the output only if its amplitude is greater than the set threshold. The gate's controls are similar to those of a compressor:

Threshold:
beyond the threshold the signal passes and reaches the output. Beneath the threshold the signal is blocked, or rather, as we will shortly see, strongly attenuated.

Range floor:
it states the amount of attenuation applied by the module (measured in dB). Values beyond -50 dB keep the gate practically closed (the equivalent of this control on the compressor is the compressor ratio).

Attack time:
amount of time taken by the gate to open when the signal goes beyond the threshold.

Hold time:
the amount of time the gate is kept open for, even after the signal has returned under the threshold.

7.18.1. Gate usages

Drum kit sound cleaning:
try and imagine the sounds coming from the microphones picking up a drum kit. Every microphone will pick up the sound of the drum kit component it is pointed towards but also the noise that all the other components produce (this phenomenon is called leaking). All these disturbances risk ruining the overall sound because each component shall be equalized according to its own characteristics. Therefore when equalizing a component, the background noises of the others shall be wrongly equalized because the eq settings are tailored for the picked up component sound, not for the ones nearby. This will add a whole load of undesired frequencies in our mix. To get rid of this noise, every single signal is sent through a gate which blocks it if the component in question isn't being played. This mops up the leaking (enjoyed the pun?) quite well though not entirely. In fact, when a certain component is played, the signal is let through the gate together with all the background sounds. However, seeing that the component's sound is predominant, it will tend to cover most of the background noises.

Noise cleaning:
a gate is effective on any signal affected by background noises and hiss in order to avoid their presence in the mix when the signal is absent.

The following is the sound of a snare drum before and after the application of a gate.

Drum kit snare drum [Track 41]

Drum kit snare drum with gate [Track 42]

Reinforcement of a drum kit's bass drum with an oscillator:
it sometimes happens to record a bass drum whose sound is a bit dull. Is it the microphone's fault? Has it been positioned badly? Is it the instrument? The musician himself? How many directions we can point our finger in, eh? Regardless of whose fault it is, one way to resolve the problem is to add a few of the lower frequencies that are missing on the bass drum's sound. To do this the following configuration shall take place:

Reinforcement of a drum kit's bass drum with an oscillator

Let's take an oscillator and let's select the frequency we'd like to add to the bass drum. Now let's send this frequency through a gate whose sidechain input is controlled by the bass drum's signal. Let's mix the two signals: bass drum and oscillator frequency at the gate's output. Basically, every time the bass drum is kicked it will produce an opening in the gate with a consequent passage of the signal from the oscillator. It is important to adjust the release time in order to allow the gate to close when the bass drum's sound ceases.

The following is the sound of a bass drum before and after the application of an oscillator commanded by a gate's signal. Notice how the original sound has been applied to another gate to clean it of other sounds coming from the drum kit.